Space Shuttle Discovery Set to Launch March 11

Space shuttle Discovery rests on Launch Pad 39A after a seven-hour rollout from the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida on Jan. 14, 2009. The shuttle is slated to launch no earlier March 12.Credit: NASA/Troy Cryder.

After
weeks of delays due to fuel valve concerns, NASA?s space shuttle Discovery is officially
set to blast off on March 11, the space agency announced Friday.

Mission
managers set the Wednesday launch date during a Flight Readiness Review at
NASA?s Kennedy Space Center in Florida, where they decided the evidence was
firm enough that suspect
fuel valves should pose no problem for Discovery's
planned flight.

"They
felt they had all the data and information they needed to support launching on
March 11," NASA spokesman Allard Beutel told SPACE.com. "All
the extra testing gave engineers confidence enough to schedule a launch
date."

Discovery
is now officially poised to lift off for its STS-119 mission from a seaside
launch pad at the Kennedy Space Center in Cape Canaveral, Fla., on Wednesday at
9:20 p.m. EDT (0120 March 12 GMT). Commander Lee Archambault will lead a crew
of seven astronauts on a two-week construction flight to the International
Space Station to deliver a new set of solar array wings.

Fuel
valve delays

Originally
slated to launch Feb. 12, Discovery?s mission has been repeatedly delayed over
concerns that the shuttle?s three fuel control valves might be faulty. The
valves function like pop-up lawn sprinklers to route gaseous hydrogen through
plumbing lines that lead to a hydrogen reservoir in the shuttle?s attached
external fuel tank. They ensure the spacecraft?s reservoir of liquid hydrogen
propellant is properly pressurized during launch.

The
concerns arose after a valve on NASA?s shuttle Endeavour cracked and chipped
during its November 2008 launch. The damage did not affect Endeavour?s launch
into orbit, but NASA wanted to be sure a similar problem would not endanger Discovery
or its astronaut crew.

"We
completed a lot of testing and a lot of analysis to understand the risks,"
said Bill Gerstenmaier, NASA?s associate administrator for space operations, in
a briefing today. "We're fully ready to go fly. It's time to step back from
the issue of the day and think about all the other things we need for flight
readiness."

NASA
ordered a series of tests on the valves, and developed a new way to examine
them to search for any signs of cracks. The new method, which involves placing
a valve in a magnetic field and measuring the strength of the field around it,
revealed cracks much tinier than the width of a hair in some of the valves.
After screening the three valves on Discovery, the mission management team
decided to replace them with new valves that had been found to have no defects.

Engineers
also thoroughly modeled what would happen to the shuttle if any of the valves
did crack during the launch, and found the chances of any serious damage to the
orbiter were very remote.

"We're
putting valves in the vehicle that have no cracks," said John Shannon,
NASA space shuttle program manager. "We also showed the risk on the
consequence side went down significantly from what we were speculating it would
be a couple weeks ago."

Launch
windows

During
Discovery's
planned 14-day mission, the astronauts are due to install the new solar
arrays to outfit the space station with enough power to run science experiments
and support new, expanded long-duration crews of six. The mission is set to
feature four spacewalks.

However,
if the team is forced to delay Discovery's launch date because of weather,
managers may decide to remove up to two spacewalks from the flight to shorten
it, allowing them to launch as late as March 16. The spacewalks, or EVAs,
wouldn't be cancelled, but just rescheduled for later missions.

"We
could give those EVAs up if we needed to get more launch time," Shannon
said.

Discovery's
crew includes pilot Tony Antonelli and mission specialists Joseph Acaba, Steve
Swanson, Richard Arnold, and John Phillips. Japan Aerospace Exploration Agency
astronaut Koichi Wakata will also ride aboard Discovery to take up position as
a new flight engineer for the space station's Expedition 18. He will relieve
NASA astronaut Sandra Magnus, who has been on the station for more than four
months. Wakata is set to return to Earth aboard next station shuttle mission,
STS-127, which is targeted to launch in June 2009.